Two important attributes of this module are __depends__ and __recommends__
dictionaries that indicates what should be installed (and each version if
necessary) for the cube to work.

Dependency on other cubes are expected to be of the form ‘cubicweb-<cubename>’.

When an instance is created, dependencies are automatically installed, while
recommends are not.

Recommends may be seen as a kind of ‘weak dependency’. Eg, the most important
effect of recommending a cube is that, if cube A recommends cube B, the cube B
will be loaded before the cube A (same thing happend when A depends on B).

Having this behaviour is sometime desired: on schema creation, you may rely on
something defined in the other’s schema; on database creation, on something
created by the other’s postcreate, and so on.

This is standard setuptools based setup module which reads most of its data
from __pkginfo__.py. In the setup function call, it should also
include an entry point definition under the cubicweb.cubes group so that
CubicWeb can discover cubes (in particular their custom cubicweb-ctl
commands):